A beauty competition at Stormont has been thrown into doubt after two politicians withdrew as judges.

In U-turns any catwalk model would be proud of, the UUP MLA Jo-Anne Dobson and the SDLP's Dolores Kelly quit as judges of the Miss Ulster competition.

Both said they didn't realise the women taking part had to meet strict criteria.

Ms Dobson said she would never have agreed to help judge the event this Saturday had she known those taking part had to comply with Miss Universe competition rules stating entrants must be aged 18 to 24, be at least 5ft 7in tall and dress size eight to 12.

Ms Kelly also withdrew, claiming to have been unaware of the dress size restriction. Both women were judges in 2011.

This weekend's event, at the seat of Northern Ireland's government, has been sponsored by NI21 leader Basil McCrea MLA. It features 11 finalists – just one is a size 12. Sinn Fein spokeswoman on women's issues, Megan Fearon MLA, branded the event "embarrassing" and "discriminatory".

UUP leader Mike Nesbitt called the dress size rules "bizarre".

His wife, broadcaster Lynda Bryans, is also a past judge.

Ms Dobson said: "I was not aware that this competition excluded anyone from entry and, had I known this, I would not have agreed to take part. Whilst I have no issues with modelling as a career, Parliament Buildings is all about inclusivity."

Ms Kelly said she had lent her support to Miss Ulster as it was a showcase for students from Belfast Metropolitan College who design the dresses, style contestants' hair and put on their make-up.

"However, I was unaware that there is a restriction on the dress size of women," she said. "I would be happy to work with colleagues on a cross-party basis to sponsor some other event that would allow the showcasing of the work and talents of young people from Belfast Met."

Event organiser Michelle McTernan said both MLAs had been aware of the competition criteria.

She said: "While I respect their decision to withdraw from the judging panel, I am disappointed that they feel they cannot continue their support.

"The negative publicity this event has sadly attracted in the media has made it politically difficult for Ms Kelly and Ms Dobson to participate now and I have every sympathy for the position they find themselves in."

NI21 leader Basil McCrea said the media has shown support to Miss Northern Ireland Meagan Green and wondered how the Miss Ulster event was any different.

A spokeswoman for Miss Northern Ireland, run by Alison Clarke of ACA Models.com, said it follows Miss World guidelines and while there are no restrictions on size or height, entrants must be single, with no children and aged 17-24.

Alliance MLA Anna Lo also criticised the plans. She said: "We should not be encouraging girls and young women to think they are only deemed beautiful if they look a certain way."